To reduce the emission, such as the local emission of motor vehicles, hybrid electric or purely electric drive concepts are being increasingly developed. The operation of electric machines in engine and generator modes requires an electrical energy store in the vehicle.
In order to improve the energy densities or the energy content of the energy store over conventional lithium ion batteries, for example, metal-oxygen batteries or metal-oxygen accumulators are promising. Here, lithium-air batteries and zinc-air batteries are known, using which high energy densities may already be obtained.
Common gas diffusion cathodes for metal-air batteries of this type have a current collector which may be an expanded aluminum metal or a porous nickel foam. A carbon/binder mixture may be introduced into the current collector as the active material. This may, for example, take place by pressing or penetration with the aid of ultrasound.
Nowadays, the gas diffusion electrode is thus prepared in most cases by applying a paste which may contain carbon, a binder, and additives. These pastes are applied to the nickel foam or alternatively to the expanded metal, e.g., aluminum. The nickel foam may, for example, be immersed into the paste for this purpose, the pores of the metal foam, in most cases in a magnitude of 0.5 mm to 1.0 mm, filling up under the ultrasound treatment. A carbon-based adhesive may be applied to coat expanded metal. The actual active paste is scraped onto a polymer foil and is thermally transferred into the expanded metal during a relaminating process. In this way, the active layer is distributed across the entire thickness in the case of a cathode structure produced in this manner. Therefore, the electrochemical oxygen reduction takes place at the oxygen/cathode boundary surface and also at the electrolyte/cathode boundary.
With the aid of conventional metal-oxygen accumulators, capacities in a range of 700 mAh/g to 800 mAh/g are achievable with reference to the active cathode mass including carbon, a binder, and other additives. However, drops in capacity, in some cases already after a few charging/discharging cycles, up to approximately 300 mAh/g and below, are often possible depending on the configuration of the battery.